A Victorian man who shot his friend's girlfriend in the head, dumped her body down a mineshaft and set her on fire has been found guilty of her murder.

Wayne Marmo, 25, had tried to claim he was not complicit in the actions of Simone Quinlan's boyfriend Brendan Neil, who allegedly beat and attacked her with a hammer at Melton before Marmo disposed of her body in August 2015.

During the trial, defence lawyer Scott Johns argued it was most likely Neil's actions that had killed Ms Quinlan, and that she was likely already dead when Marmo shot her.

He said Marmo was instead guilty of the lesser crime of attempted murder.

Simone Quinlan.

The court previously heard that Marmo and two other friends arrived at Neil's house during his attack on Ms Quinlan to exchange stolen chainsaws for the drug ice.

The three sat around the kitchen table smoking ice while the attack against Ms Quinlan escalated, and Marmo began sawing the barrel off a .22 rifle.

He then reversed his Hilux towards the house, with Neil placing Ms Quinlan's body - wrapped in a blanket - inside the tray.

Neil then left the premises and the other three drove the woman's body to a mineshaft at Kangaroo Flat, near Bendigo.

Along the way, Marmo pulled over and shot the mother-of-two in the head about five times.

Last week, the court heard Ms Quinlan had issued a "very scared" statement to police just days before her death.

In it she explained how her boyfriend was violent towards her and had once hit her in the head with a baseball bat.

She had sent "urgent" Facebook messages to friends in the days leading up to her death, telling them she'd been living in a disused kindergarten and asking for help.

Marmo was found guilty by a jury in the Supreme Court of Victoria on Monday and remanded in custody until May 18 for further mention.